This invention relates, in general, to power generation from piezoelectric materials, and particularly to an improved DC bias scheme for improved efficiency use of various electrostrictive materials for piezoelectric power generation.
A recent development in the field of piezoelectric power generation from natural sources of energy and the like is the use of "field-induced piezoelectricity" in electrostrictive materials. Typically, electrostrictive materials have very weak piezoelectric characteristics (related to a materials parameter known as d.sub.31). However, if a DC bias is applied across the materials, e.g., by means of a pair of electrodes on opposite surfaces of an electrostrictive material such as polyurethane, the piezoelectric characteristics can be significantly increased and in proportion to the DC bias.
Circuit arrangements for applying a DC bias between electrodes are well known. In general, a DC bias voltage is applied through a large bias resistance serving to prevent significant DC current flow within the biasing circuit. A problem, however, is that the bias resistor in known arrangements is in parallel with the load of the generator system and, particularly in those instances where the load resistance is quite highs a significant portion of the AC power generated by the system is lost in the bias circuit.